Power surface mount light emitting die package

ABSTRACT

A light emitting die package is disclosed. The die package includes a substrate, a reflector plate, and a lens. The substrate may be made from thermally conductive but electrically insulating material or from a material that is both thermally and electrically conductive. In embodiments wherein the substrate is made from an electrically conductive material, the substrate further includes an electrically insulating, thermally conductive material formed on the electrically conductive material. The substrate has traces for connecting to a light emitting diode (LED) at a mounting pad. The reflector plate is coupled to the substrate and substantially surrounds the mounting pad. The lens substantially covers the mounting pad. Heat generated by the LED during operation is drawn away from the LED by both the substrate (acting as a bottom heat sink) and the reflector plate (acting as a top heat sink). The reflector plate includes a reflective surface to direct light from the LED in a desired direction.

RELATED APPLICATIONS

[0001] The present application is a continuation-in-part of U.S. patentapplication Ser. No. 10/446,532 entitled “Power Surface Mount LightEmitting Die Package” filed May 27, 2003, which claims the benefit ofU.S. Provisional Application Serial No. 60/408,254 entitled “Power-SMT,LED Package with Dual Heat-Sinks and an Optical System orChemical-Coated Lens” filed Sep. 4, 2002.

BACKGROUND

[0002] The present invention relates to the field of packagingsemiconductor devices, and more particularly to packaging light emittingdiodes.

[0003] Light emitting diodes (LEDs) are often packaged within leadframepackages. A leadframe package typically includes a molded plastic bodywhich encapsulates an LED, a lens portion, and thin metal leadsconnected to the LED and extending outside the plastic body. The metalleads of the leadframe package serve as the conduit to supply the LEDwith electrical power and, at the same time, may act to draw heat awayfrom the LED. Heat is generated by the LED when power is applied to theLED to produce light. A portion of the leads extends out from thepackage body for connection to circuits external to the leadframepackage.

[0004] Some of the heat generated by the LED is dissipated by theplastic package body; however, most of the heat is drawn away from theLED via the metal components of the package. The metal leads aretypically very thin and have a small cross section. For this reason,capacity of the metal leads to remove heat from the LED is limited. Thislimits the amount of power that can be sent to the LED thereby limitingthe amount of light that can be generated by the LED.

[0005] To increase the capacity of an LED package to dissipate heat, inone LED package design, a heat sink slug is placed under the metal leadswithin the LED package. The heat sink slug increases the capacity of theLED package to dissipate heat; however, the heat sink slug increases thesize, the mass, and the cost of the LED package. Increases in the size,the mass, and the cost are undesirable.

[0006] In another LED package design, the leads of the leadframe areextended (in various shapes and configurations) beyond the immediateedge of the LED package body. This increases the surface area of theportions of the leads exposed to the surrounding air. The increasedexposed surface area of the extended leads increases the capacity of theLED package to dissipate heat; however, the extended leads increase thesize, the mass, and the cost of the LED package.

[0007] Another undesirable aspect of the current leadframe packagedesign relates to problems associated with thermal expansion of thepackage. When heat is generated, the LED package experiences thermalexpansion. Each of the parts of the LED package has a differentcoefficient of thermal expansion (CTE). For example, the CTE of the LED,the CTE of the package body, the CTE of the leads, and the CTE of lensare different from each other. For this reason, when heated, each ofthese parts experience different degrees of thermal expansion resultingin mechanical stresses between the parts of the package therebyadversely affecting its reliability.

[0008] Consequently, there remains a need for an improved LED packagethat overcomes or alleviates one or more of the shortcomings of theprior art packages.

SUMMARY

[0009] Embodiments of the present invention provide a package for asemiconductor die such as a light emitting diode, the package includinga substrate having electrically conductive elements for connecting to alight emitting diode at a mounting pad, a reflector plate coupled to thesubstrate and substantially surrounding the mounting pad, and lenssubstantially covering the mounting pad.

[0010] Other embodiments of the present invention provide asemiconductor die package which includes a bottom heat sink and a topheat sink. The bottom heat sink may have traces on its top surface. Asemiconductor chip may be mounted on the top surface of the bottom heatsink and electrically connected to the traces. The top heat sink may bemechanically coupled to the bottom heat sink.

[0011] In other embodiments, the bottom heat sink may include athermally and electrically conductive plate having first and secondsurfaces. The plate may comprise a metal such as copper, aluminum oralloys of either. A thin, thermally conductive insulating film is formedon portions of the first surface of the metal plate and may be formed onother surfaces of the metal plate.

[0012] Conductive elements such as metal traces and/or metal leads maybe formed on the ceramic/polymer film. Since the ceramic/polymer film isinsulating, the conductive traces are not in electrical contact with themetal plate. The conductive element may form or be electricallyconnected to a mounting pad adapted to receive an electronic device suchas an LED.

[0013] In some embodiments, one or more via holes may be formed throughthe substrate. In some embodiments, the via holes may be coatedinternally with an insulating material such as the ceramic/polymer film.Electrical conductors such as electrically conductive traces may beformed in the via holes to electrically connect conductive elements onthe first surface of the substrate to conductive elements on the secondsurface of the substrate.

[0014] A substrate according to embodiments of the present invention mayalso include electronic circuitry such as a zener diode and/or aresistor network connected between one or more conductive elements forelectro-static discharge (ESD) and/or over-voltage protection.

[0015] Other aspects and advantages of the present invention will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, illustrating by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1A is a perspective view of a semiconductor die packageaccording to one embodiment of the present invention;

[0017]FIG. 1B is an exploded perspective view of the semiconductorpackage of FIG. 1A;

[0018]FIG. 2A is a top view of a portion of the semiconductor package ofFIG. 1A;

[0019]FIG. 2B is a side view of a portion of the semiconductor packageof FIG. 1A;

[0020]FIG. 2C is a front view of a portion of the semiconductor packageof FIG. 1A;

[0021]FIG. 2D is a bottom view of a portion of the semiconductor packageof FIG. 1A;

[0022]FIG. 3 is a cut-away side view of portions of the semiconductorpackage of FIG. 1A;

[0023]FIG. 4 is a side view of the semiconductor package of FIG. 1A withadditional elements;

[0024]FIG. 5 an exploded perspective view of a semiconductor die packageaccording to another embodiment of the present invention;

[0025]FIG. 6A is a top view of a portion of the semiconductor package ofFIG. 5;

[0026]FIG. 6B is a side view of a portion of the semiconductor packageof FIG. 5;

[0027]FIG. 6C is a front view of a portion of the semiconductor packageof FIG. 5;

[0028]FIG. 6D is a bottom view of a portion of the semiconductor packageof FIG. 5;

[0029]FIG. 7A is a top view of a portion of a semiconductor packageaccording to another embodiments of the present invention;

[0030]FIG. 7B is a front view of the portion of a semiconductor packageof FIG. 7A;

[0031]FIG. 7C is a cut-away front view of the portion of a semiconductorpackage of FIG. 7A taken along line A-A;

[0032]FIG. 8 is a side view of a portion of a semiconductor packageaccording to another embodiment of the present invention;

[0033]FIG. 9 is a side view of a portion of a semiconductor packageaccording to another embodiment of the present invention;

[0034]FIG. 10A is a top view of a portion of a semiconductor packageaccording to another embodiments of the present invention; and

[0035]FIG. 10B is a top view of a portion of a semiconductor packageaccording to anther embodiments of the present invention.

DETAILED DESCRIPTION

[0036] The present invention will now be described with reference to theFIGS. 1 through 10B, which illustrate various embodiments of the presentinvention. As illustrated in the Figures, the sizes of layers or regionsare exaggerated for illustrative purposes and, thus, are provided toillustrate the general structures of the present invention. Furthermore,various aspects of the present invention are described with reference toa layer or structure being formed on a substrate or other layer orstructure. As will be appreciated by those of skill in the art,references to a layer being formed “on” another layer or substratecontemplates that additional layers may intervene. References to a layerbeing formed on another layer or substrate without an intervening layerare described herein as being formed “directly on” the layer orsubstrate. Furthermore, relative terms such as beneath may be usedherein to describe one layer or regions relationship to another layer orregion as illustrated in the Figures. It will be understood that theseterms are intended to encompass different orientations of the device inaddition to the orientation depicted in the Figures. For example, if thedevice in the Figures is turned over, layers or regions described as“beneath” other layers or regions would now be oriented “above” theseother layers or regions. The term “beneath” is intended to encompassboth above and beneath in this situation. Like numbers refer to likeelements throughout.

[0037] As shown in the figures for the purposes of illustration,embodiments of the present invention are exemplified by a light emittingdie package including a bottom heat sink (substrate) having traces forconnecting to a light emitting diode at a mounting pad and a top heatsink (reflector plate) substantially surrounding the mounting pad. Alens covers the mounting pad. In effect, the die package according tosome embodiments of the present invention comprises a two part heat sinkwith the bottom heat sink utilized (in additional to its utility fordrawing and dissipating heat) as the substrate on which the LED ismounted and connected, and the top heat sink utilized (in additional toits utility for drawing and dissipating heat) as a reflector plate todirect light produced by the LED. Because both the bottom and the topheat sinks draw heat away from the LED, more power can be delivered tothe LED, and the LED can thereby produce more light.

[0038] Further, in the present invention, the die package itself may actas the heat sink removing heat from the LED and dissipating it. For thisreason, the LED die package of the present invention may not requireseparate heat sink slugs or leads that extend away from the package.Accordingly, an LED die package according to the present invention maybe more compact, more reliable, and less costly to manufacture than adie package of the prior art.

[0039]FIG. 1A is a perspective view of a semiconductor die package 10according to one embodiment of the present invention and FIG. 1B is anexploded perspective view of the semiconductor package of FIG. 1A.Referring to FIGS. 1A and 1B, the light emitting die package 10 of thepresent invention includes a bottom heat sink 20, a top heat sink 40,and a lens 50.

[0040] The bottom heat sink 20 is illustrated in more detail in FIGS. 2Athrough 2D. FIGS. 2A, 2B, 2C, and 2D provide, respectively, a top view,a side view, a front view, and a bottom view of the bottom heat sink 20of FIG. 1A. Further, FIG. 2C also shows an LED assembly 60 in additionto the front view of the bottom heat sink 20. The LED assembly 60 isalso illustrated in FIG. 1B. Referring to FIGS. 1A through 2D, thebottom heat sink 20 provides support for electrical traces 22 and 24;for solder pads 26, 32, and 34; and for the LED assembly 60. For thisreason, the bottom heat sink 20 is also referred to as a substrate 20.In the Figures, to avoid clutter, only representative solder pads 26,32, and 34 are indicated with reference numbers. The traces 22 and 24and the solder pads 26, 32, and 34 can be fabricated using conductivematerial. Further, additional traces and connections can be fabricatedon the top, side, or bottom of the substrate 20, or layered within thesubstrate 20. The traces 22 and 24, the solder pads 26, 32, and 34, andany other connections can be interconnected to each other in anycombinations using known methods, for example via holes.

[0041] In some embodiments, the substrate 20 may be made of materialhaving high thermal conductivity but is electrically insulating, forexample, aluminum nitride (AlN) or alumina (Al₂O₃). In otherembodiments, such as the embodiments described below in connection withFIGS. 7A through 10B, the substrate 20 may comprise a material that isboth electrically and thermally conductive. In such embodiments, themetal leads, conductive traces 22 and 24, or both may be insulated fromthe substrate by means of an insulating film formed on portions of thesubstrate as described in more detail below. Dimensions of the substrate20 can vary widely depending on application and processes used tomanufacture the die package 10. For example, in the illustratedembodiment, the substrate 20 may have dimensions ranging from fractionsof millimeters (mm) to tens of millimeters. Although the presentinvention is not limited to particular dimensions, one specificembodiment of the die package 10 of the present invention is illustratedin Figures having the dimensions denoted therein. All dimensions shownin the Figures are in millimeters (for lengths, widths, heights, andradii) and degrees (for angles) except as otherwise designated in theFigures, in the Specification herein, or both.

[0042] The substrate 20 has a top surface 21, the top surface 21including the electrical traces 22 and 24. The traces 22 and 24 provideelectrical connections from the solder pads (for example top solder pads26) to a mounting pad 28. The top solder pads 26 may comprise portionsof the traces 22 and 24 generally proximal to sides of the substrate 20.The top solder pads 26 are electrically connected to side solder pads32. The mounting pad 28 is a portion of the top surface (includingportions of the trace 22, the trace 24, or both) where the LED assembly60 is mounted. Typically the mounting pad 28 is generally locatedproximal to center of the top surface 21. In alternative embodiments ofthe present invention, the LED assembly 60 can be replaced by othersemiconductor circuits or chips.

[0043] The traces 22 and 24 provide electrical routes to allow the LEDassembly 60 to electrically connect to the solder pads 26, 32, or 34.Accordingly, some of the traces are referred to as first traces 22 whileother traces are referred to as second traces 24. In the illustratedembodiment, the mounting pad 28 includes portions of both the firsttraces 22 and the second traces 24. In the illustrated example, the LEDassembly 60 is placed on the first trace 22 portion of the mounting pad28 thereby making contact with the first trace 22. In the illustratedembodiment, top of the LED assembly 60 and the second traces 24 areconnected to each other via a bond wire 62. Depending on theconstruction and orientation of LED assembly 60, first traces 22 mayprovide anode (positive) connections and second traces 24 may comprisecathode (negative) connections for the LED assembly 60 (or vice versa).

[0044] The LED assembly 60 can include additional elements. For example,in FIGS. 1B and 2C, the LED assembly 60 is illustrated including the LEDbond wire 62, an LED subassembly 64, and a light emitting diode (LED)66. Such LED subassembly 64 is known in the art and is illustrated forthe purposes of discussing the invention and is not meant to be alimitation of the present invention. In the Figures, the LED assembly 60is shown die-attached to the substrate 20. In alternative embodiments,the mounting pad 28 can be configured to allow flip-chip attachment ofthe LED assembly 60. Additionally, multiple LED assemblies can bemounted on the mounting pad 28. In alternative embodiments, the LEDassembly 60 can be mounted over multiple traces. This is especially trueif flip-chip technology is used.

[0045] The topology of the traces 22 and 24 can vary widely from thetopology illustrated in the Figures while still remaining within thescope of the present invention. In the Figures, three separate cathode(negative) traces 24 are shown to illustrate that three LED assembliescan be placed on the mounting pad 28, each connected to a differentcathode (negative) trace; thus, the three LED assemblies may beseparately electrically controllable. The traces 22 and 24 are made ofconductive material such as gold, silver, tin, or other metals. Thetraces 22 and 24 can have dimensions as illustrated in the Figures andhaving thickness in the order of microns or tens of microns depending onapplication. For example, the traces 22 and 24 can be 15 microns thick.FIGS. 1A and 2A illustrate an orientation marking 27. Such markings canbe used to identify the proper orientation of the die package 10 evenafter assembling the die package 10. The traces 22 and 24, asillustrated, can extend from the mounting pad 28 to sides of thesubstrate 20.

[0046] Continuing to refer to FIGS. 1A through 2D, the substrate 20defines semi-cylindrical spaces 23 and quarter-cylindrical spaces 25proximal to its sides. In the Figures, to avoid clutter, onlyrepresentative spaces 23 and 25 are indicated with reference numbers.The semi-cylindrical spaces 23 and the quarter-cylindrical spaces 25provide spaces for solder to flow-through and solidify-in when the diepackage 10 is attached to a printed circuit board (PCB) or anotherapparatus (not shown) to which the die package 10 is a componentthereof. Moreover, the semi-cylindrical spaces 23 and thequarter-cylindrical spaces 25 provide convenient delineation and breakpoints during the manufacturing process.

[0047] The substrate 20 can be manufactured as one individual section ofa strip having a plurality of adjacent sections, each section being asubstrate 20. Alternatively, the substrate 20 can be manufactured as oneindividual section of an array of sections, the array having multiplerows and columns of adjacent sections. In such configuration, thesemi-cylindrical spaces 23 and quarter-cylindrical spaces 25 can beutilized as handles for the strip or the array during the manufacturingprocess.

[0048] Further, the semi-cylindrical spaces 23 and thequarter-cylindrical spaces 25, combined with scribed grooves or otheretchings between the sections, assist in separating each individualsubstrate from the strip or the wafer. The separation can beaccomplished by introducing physical stress to the etched lines(crossing the semi-cylindrical spaces 23 and the quarter-cylindricalspaces 25) by bending the strip or the wafer. These features simplifythe manufacturing process thus reducing costs by eliminating the needfor special carrier fixtures to handle the strip or the wafer during themanufacturing process. Further, the semi-cylindrical spaces 23 and thequarter-cylindrical spaces 25 may serve as via holes connecting the topsolder pads 26, the side solder pads 32, and the bottom solder pads 34.

[0049] The substrate 20 has a bottom surface 29 including a thermalcontact pad 36. The thermal contact pad can be fabricated using materialhaving high heat conductivity such as gold, silver, tin, or othermaterial including but not limited to precious metals.

[0050]FIG. 3 illustrates a cut-away side view of portions of thesemiconductor package of FIGS. 1A and 1B. In particular, the FIG. 3illustrates a cut-away side view of the top heat sink 40 and the lens50. Referring to FIGS. 1A, 1B, and 3, the top heat sink 40 is made frommaterial having high thermal conductivity such as aluminum, copper,ceramics, plastics, composites, or a combination of these materials. Ahigh temperature, mechanically tough, dielectric material can be used toovercoat the traces 22 and 24 (with the exception of the centraldie-attach area) to seal the traces 22 and 24 and provide protectionfrom physical and environmental harm such as scratches and oxidation.The overcoating process can be a part of the substrate manufacturingprocess. The overcoat, when used, also insulates the substrate 20 fromthe top heat sink 40. The overcoat may then covered with a hightemperature adhesive such as thermal interface material manufactured byTHERMOSET that bonds the substrate 20 with the top heat sink 40.

[0051] The top heat sink 40 may include a reflective surface 42substantially surrounding the LED assembly 60 mounted on the mountingpad 28 (of FIGS. 2A and 2C). The reflective surface 42 reflects portionsof light from the LED assembly 60 as illustrated by sample light rays63. Other portions of the light are not reflected by the reflectivesurface 42 as illustrated by sample light ray 61. Illustrative lightrays 61 and 63 are not meant to represent light traces often use in theoptical arts. For efficient reflection of the light, the top heat sink40 is preferably made from material that can be polished, coined, orboth. Alternatively, to achieve high reflectivity, the opticalreflective surface 42 or the entire heat sink 40 can be plated ordeposited with high reflective material such as silver, aluminum, oranother substance that serves the purpose. For this reason, the top heatsink 40 is also referred to as a reflector plate 40. The reflector plate40 is made of material having high thermal conductivity if and whenrequired by the thermal performance of the package 10.

[0052] In the illustrated embodiment, the reflective surface 42 isillustrated as a flat surface at an angle, for example 45 degrees,relative to the reflective plate's horizontal plane. The presentinvention is not limited to the illustrated embodiment. For example, thereflective surface 42 can be at a different angle relative to thereflective plate's horizontal plane. Alternatively, the reflective platecan have a parabolic or another shape.

[0053] The reflective plate 40 includes a ledge 44 for supporting andcoupling with the lens 50. The LED assembly 60 is encapsulated withinthe die package 10 (of FIGS. 1A and 1B) using encapsulation material 46such as, for example only, silicone. The encapsulation material 46 ispreferably high temperature polymer with high light transmissivity andrefractive index that matches refractive index of the lens 50.

[0054] The lens 50 is made from material having high lighttransmissivity such as, for example only, glass, quartz, hightemperature plastic, or a combination of these materials. The lens 50may be placed in contact with the encapsulation material 46.Consequently, as the die package 10 is heated and experiences thermalexpansion, the lens 50 may be cushioned by the encapsulation material 46such that the lens 50 may be protected from mechanical stresses arisingfrom thermal expansion of other parts of the die package 10. In someembodiments, the lens 50 defines a shallow trough 52 which can be filledwith optical chemicals, for example, phosphors, light diffusants such ascalcium carbonate, center frequency shifting material such asfluorescent material, or a combination of these materials.

[0055]FIG. 4 illustrates the die package 10 coupled to an external heatsink 70. Referring to FIG. 4, the thermal contact pad 36 can be attachedto the external heat sink 70 using epoxy, solder, or any other thermallyconductive adhesive, electrically conductive adhesive, or thermally andelectrically conductive adhesive 74. The external heat sink 70 can be aprinted circuit board (PCB) or other structure that draws heat from thedie package 10. The external heat sink can include circuit elements (notshown) or heat dissipation fins 72 in various configurations.

[0056] An embodiment of the invention having certain alternateconfiguration is shown in FIGS. 5 through 6D. Portions of this secondembodiment are similar to corresponding portions of the first embodimentillustrated in FIGS. 1A through 4. For convenience, portions of thesecond embodiment as illustrated in FIGS. 5 through 6D that are similarto portions of the first embodiment are assigned the same referencenumerals, analogous but changed portions are assigned the same referencenumerals accompanied by letter “a,” and different portions are assigneddifferent reference numerals.

[0057]FIG. 5 is an exploded perspective view of an LED die package 10 ain accordance with other embodiments of the present invention. Referringto FIG. 5, the light emitting die package 10 a of the present inventionincludes a bottom heat sink (substrate) 20 a, a top heat sink (reflectorplate) 40 a, and a lens 50.

[0058]FIGS. 6A, 6B, 6C, and 6D, provide, respectively, a top view, aside view a front view, and a bottom view of the substrate 20 a of FIG.5. Referring to FIGS. 5 through 6D, in the illustrated embodiment, thesubstrate 20 a includes one positive trace 22 a and four negative traces24 a. These traces 22 a and 24 a have are configured differently thanthe traces 22 and 24 of FIG. 2A. The substrate 20 a includes flanges 31that define latch spaces 33 for reception of legs 35 of the reflectorplate 40 a thereby mechanically engaging the reflector plate 40 a withthe substrate 20 a.

[0059] Other embodiments of the invention are illustrated in FIGS. 7Athrough 10B. According to these embodiments, a substrate for a highpower light emitting device includes a thermally and electricallyconductive plate having first and second surfaces. The plate maycomprise a metal such as copper, aluminum or alloys of either. A thin,thermally conductive insulating film is formed on the first surface ofthe metal plate. In some embodiments, the thermally conductiveinsulating film comprises a ceramic/polymer film such as the ThermalClad film available from by The Bergquist Company of Chanhassen, Minn.,USA.

[0060] Conductive elements such as metal traces and/or metal leads maybe formed on the ceramic/polymer film. Since the ceramic/polymer film isinsulating, the conductive traces are not in electrical contact with themetal plate. A conductive element may form or be electrically connectedto a mounting pad adapted to receive an electronic device. As discussedabove in connection with the embodiments illustrated in FIGS. 1-6, thetopology of the metal traces may vary widely while still remainingwithin the scope of the invention.

[0061] An LED assembly may be bonded to the mounting pad for example bymeans of soldering, thermosonic bonding or thermocompression bonding.Heat generated by the LED may be dissipated at least in part through themetal plate. Since the substrate itself may act as a heatsink, the needfor bonding an additional heatsink to the structure may be reduced oreliminated. However, an additional heatsink may be placed in thermalcommunication with the metal plate so that heat may be drawn away fromthe operating device more efficiently.

[0062] In one embodiment, one or more via holes may be formed throughthe insulating film and the metal plate. The via holes may be internallycoated with an insulating material such as the ceramic/polymer film.Electrical conductors such as electrically conductive traces may beformed in the via and may electrically connect conductive elements onthe first surface of the substrate to conductive elements on the secondsurface of the substrate. A substrate according to such an embodimentmay be mounted on a surface such as a printed circuit board without theuse of metal leads, which may result in a more mechanically robustpackage.

[0063] A substrate according to embodiments of the present invention mayalso include electronic circuitry such as a discrete zener diode and/ora resistor network for electrostatic discharge (ESD) and/or over-voltageprotection.

[0064] Although not illustrated in FIGS. 7-10, the substrate may furtherinclude features such as the semi-cylindrical and quarter-cylindricalspaces, orientation markings, side bond pads, flanges and other featuresillustrated in FIGS. 1-6.

[0065] Portions of the embodiments illustrated in FIGS. 7A through 10Bare similar to corresponding portions of the embodiments illustrated inFIGS. 1 through 6D. For convenience, portions of the embodiment asillustrated in FIGS. 7A through 10B that are similar to portions of thefirst embodiment are assigned the same reference numerals, analogous butchanged portions are assigned the same reference numerals accompanied byletter “b,” and different portions are assigned different referencenumerals.

[0066] Referring now to FIG. 7A, a substrate 20 b according to anotherembodiments of the present invention is illustrated. FIGS. 7A and 7Bprovide, respectively, a top view and a front view of the substrate 20b. Further, FIG. 7B also shows an LED assembly 60 in addition to thefront view of the substrate 20 b. The substrate 20 b includes athermally and electrically conductive plate 51 having first and secondsurfaces 51 a and 51 b. The plate 51 may comprise a metal such ascopper, aluminum or alloys of either. A thin, thermally conductiveinsulating film 48 is formed on at least portions of the first surface51 a of the metal plate 51. In some embodiments, the thermallyconductive insulating film 48 comprises a ceramic/polymer film such asthe Thermal Clad film available from by The Bergquist Company ofChanhassen, Minn., USA. In addition, a thermally conductive insulatingfilm 49 may be formed on the second surface 51 b of plate 51, as well asside surfaces.

[0067] The substrate 20 b provides support for electrically conductiveelements such as electrical traces 22 and 24; for solder pads 26 ; andfor the LED assembly 60. Further, additional traces and connections canbe fabricated on the top, side, or bottom of the substrate 20 b, orlayered within the substrate 20 b. The traces 22 and 24, the solder pads26, and any other connections can be interconnected to each other in anycombinations using known methods, for example via holes.

[0068] The substrate 20 b has a top surface 21 b, the top surface 21 bincluding the electrical traces 22 and 24. The traces 22 and 24 provideelectrical connections from the solder pads (for example top solder pads26) to a mounting pad 28. The top solder pads 26 may comprise portionsof the traces 22 and 24 generally proximal to sides of the substrate 20b. The mounting pad 28 is a portion of the top surface (includingportions of the trace 22, the trace 24, or both) where the LED assembly60 is mounted. Typically the mounting pad 28 is generally locatedproximal to center of the top surface 21 b. In alternative embodimentsof the present invention, the LED assembly 60 can be replaced by othersemiconductor circuits or chips.

[0069] The topology of the traces 22 and 24 can vary widely from thetopology illustrated in the Figures while still remaining within thescope of the present invention. In the Figures, only one cathode(negative) and one anode (positive) trace is shown. However, multiplecathode or anode traces may be included on the substrate 20 b tofacilitate the mounting of plural LED assemblies on the mounting pad 28,each connected to a different cathode or anode trace; thus, the threeLED assemblies may be separately electrically controllable. The traces22 and 24 are made of conductive material such as gold, silver, tin, orother metals.

[0070] The substrate 20 b has a bottom surface 29 b including a thermalcontact pad 36. The thermal contact pad can be fabricated using materialhaving high heat conductivity such as gold, silver, tin, or othermaterial including but not limited to precious metals.

[0071]FIG. 7C illustrates a cut-away front view of portions of thesubstrate 20 b taken along section line A-A of FIG. 7A. As shown in FIG.7C, one or more via holes 45 a, 45 b may be formed through the substrate20 b. The via holes 45 a, 45 b may be internally coated with aninsulating material such as the ceramic/polymer film. Electricalconductors such as electrically conductive traces 47 a, 47 b may beformed in the via holes and may electrically connect conductive elementson the first surface of the substrate to conductive elements on thesecond surface of the substrate. As illustrated in FIG. 7C, a conductivetrace 47 a in via hole 45 a connects trace 24 on the first side 21 b, orthe top surface 21 b, of the substrate 20 b to solder pad 34 on thesecond side 29 b, or the bottom surface 29 b, of the substrate 20 b.Likewise, a conductive trace 47 b extending through via hole 45 bconnects conductive trace 22 to a bond pad 38.

[0072] A substrate according to such an embodiment may be mounted on asurface such as a printed circuit board without the use of metal leads,which may result in a more mechanically robust package.

[0073] As discussed above, a high temperature, mechanically tough,dielectric material can be used to overcoat the traces 22 and 24 (withthe exception of the central die-attach area 28) to seal the traces 22and 24 and provide protection from physical and environmental harm suchas scratches and oxidation. The overcoating process can be a part of thesubstrate manufacturing process. The overcoat, when used, also insulatesthe traces 22 and 24 from the top heat sink 40. The overcoat may then becovered with a high temperature adhesive such as thermal interfacematerial manufactured by THERMOSET that bonds the substrate 20 b withthe top heat sink 40.

[0074] Other embodiments that do not utilize via holes are illustratedin FIGS. 8 and 9. As illustrated in FIG. 8, the conductive traces 22, 24may form or be attached to metal leads 39, 41 which extend away from thepackage and which may be mounted directly to a circuit board. In such anembodiment, only the first surface 21 b of the substrate 20 b mayinclude an electrically insulating, thermally conductive film 48.

[0075]FIG. 9 illustrates an embodiment in which conductive traces 22, 24extend down the sidewalls of the substrate 20 b to contact bond pads 34and 38 on the second surface of the substrate 20 b. Such a configurationmay permit the package to be mounted directly onto a circuit boardwithout the use of metal leads or via holes.

[0076] As illustrated in FIGS. 10A and 10B, the substrate 20 b may beconfigured to include electronic circuitry such as a discrete zener 65diode, a resistor network 67, other electronic elements, or anycombination of these. Such electronic circuitry can be connected betweenthe traces 22 and 24 which may operate as anode/or cathode elements. Theelectronic circuitry can be used for various purposes, for example, toprevent electro-static discharge (ESD), for over-voltage protection, orboth. In the illustrated examples, the zener diode D1 65 connectedbetween the trace 22 and the trace 24 as illustrated in FIG. 10B mayprevent an excessive reverse voltage from being applied to anoptoelectronic device mounted on the substrate 20 b. Similarly, theresistor network 67 such as printed resistor 67 may provide ESDprotection to a device mounted on the sbustrate 20.

[0077] From the foregoing, it will be apparent that the presentinvention is novel and offers advantages over the current art. Althoughspecific embodiments of the invention are described and illustratedabove, the invention is not to be limited to the specific forms orarrangements of parts so described and illustrated. For example,differing configurations, sizes, or materials may be used to practicethe present invention. The invention is limited by the claims thatfollow. In the following, claims drafted to take advantage of the “meansor steps for” provision of 35 USC section 112 are identified by thephrase “means for.”

What is claimed is:
 1. A light emitting die package comprising: asubstrate comprising an electrically and thermally conductive materialand having a first surface; a thermally conductive, electricallyinsulating film covering at least a portion of said first surface; afirst conductive element on said insulating film, said conductiveelement insulated from said substrate by said insulating film; a secondconductive element on said insulating film, said second conductiveelement spaced apart from said first conductive element and electricallyinsulated from said substrate by said insulating film wherein at leastone of said first and second conductive elements comprises a mountingpad for mounting a light emitting die thereon; a reflector plate coupledto said substrate and substantially surrounding the mounting pad; and alens substantially covering the mounting pad.
 2. The light emitting diepackage recited in claim 1 further comprising a light emitting diode(LED) mounted on said substrate and connected to the first and secondconductive elements.
 3. The light emitting die package recited in claim2 wherein the LED is encapsulated within optically clear polymer.
 4. Thelight emitting die package recited in claim 1 wherein said first andsecond conductive elements comprise metal traces.
 5. The light emittingdie package recited in claim 1 wherein said substrate comprises a metal.6. The light emitting die package recited in claim 5, wherein saidsubstrate comprises a metal selected from the group consisting of copperand aluminum.
 7. The light emitting die package recited in claim 5,wherein said substrate comprises a copper/aluminum alloy.
 8. The lightemitting die package recited in claim 1 wherein said insulating filmcomprises a ceramic polymer film.
 9. The light emitting die packagerecited in claim 1, wherein said substrate comprises a second surfaceopposite said first surface, and further comprising at least on via holethrough said substrate.
 10. The light emitting die package recited inclaim 9, wherein the surface of said via hole is coated with aninsulating film coating.
 11. The light emitting die package recited inclaim 10, wherein said via hole includes a conductive tracetherethrough, said conductive trace is insulated from said substrate bysaid insulating film coating, and said conductive trace is in electricalcontact with one of said first and second conductive leads.
 12. Thelight emitting die package recited in claim 9 wherein said secondsurface of said substrate includes a thermally conductive insulatingfilm on at least a portion of said second surface and wherein saidpackage further comprises a third electrical lead on said secondsurface, said third electrical lead is insulated from said substrate bysaid thermally conductive insulating film and said third electrical leadis in electrical contact with said conductive trace through said viahole.
 13. The light emitting die package recited in claim 1 furthercomprising an external heat sink coupled to said substrate.
 14. Thelight emitting die package recited in claim 13 wherein said substratehas a bottom side plated with metals for coupling with said externalheat sink.
 15. The light emitting die package recited in claim 1 whereinat least one conductive element extends from the mounting pad to a sideof said substrate.
 16. The light emitting die package recited in claim 1wherein said substrate comprises flanges along at least one side formechanically engaging said reflector plate.
 17. The light emitting diepackage recited in claim 1 wherein said reflector plate substantiallysurrounds the mounting pad.
 18. The light emitting die package recitedin claim 1 wherein said reflector plate defines a reflection surface.19. The light emitting die package recited in claim 1 wherein saidreflector plate comprises material having high thermal conductivity. 20.The light emitting die package recited in claim 1 wherein said reflectorplate comprises at least one leg mechanically engaging said substratefor increased thermal transfer.
 21. The light emitting die packagerecited in claim 1 wherein said lens comprises a trough adapted toreceive optical chemicals.
 22. The light emitting die package recited inclaim 1 wherein said lens comprises frequency shifting compounds. 23.The light emitting die package recited in claim 1 wherein said lenscomprises diffusant.
 24. The light emitting die package recited in claim1 wherein said lens comprises a phosphor.
 25. A light emitting diepackage comprising: a metal substrate having a first surface; anelectrically insulating film covering at least a portion of said firstsurface; a first conductive trace on said insulating film, saidconductive trace insulated from said substrate by said insulating film;a mounting pad for mounting a light emitting device, said mounting padelectrically connected to said first conductive trace; a reflector platecoupled to said substrate and substantially surrounding the mountingpad; and a lens substantially covering the mounting pad.
 26. A lightemitting die package comprising: a metal substrate having a firstsurface; a conductive trace on said first surface, said conductive traceinsulated from said metal substrate by an insulating film; saidconductive trace forming a mounting pad for mounting a light emittingdevice; and a metal lead electrically connected to said conductive traceand extending away from said first surface.
 27. A light emitting diepackage comprising: a metal substrate having a first surface and asecond surface opposite said first surface; a via hole through saidsubstrate; a conductive trace extending from said first surface to saidsecond surface, said conductive trace insulated from said metalsubstrate by insulating film; and a metal contact pad on one of saidfirst and second surfaces electrically connected to said conductivetrace.